Currently, medical devices to be placed in the human body, such as implantable pacemakers which correct abnormal movements of the human heart and implantable heart defibrillators, are in practical use. For example, in an implantable pacemaker, a feedthrough terminal is provided on a casing containing a battery, a circuit board, and the like, and an electrode of the feedthrough terminal is connected to a lead which is surgically connected to an appropriate region of the heart. The battery and the circuit board in the casing should not be brought into contact with the tissues of the human body, and the feedthrough is required to reliably prevent bodily fluids from entering the casing in order to prevent operation failures of the pacemaker due to adhesion of bodily fluids to the circuit board and the battery. At the same time, the feedthrough is required to be composed of a highly biocompatible, safe material that does not affect the functions of the human body even if it comes into contact with bodily fluids.
An example of such a feedthrough that is applicable to the living body is described, for example, in Patent Literature 1. In the feedthrough of Patent Literature 1, a housing mainly composed of titanium (Ti) which is a highly biocompatible metal is joined to and surrounds a ceramic member composed of alumina. Through-holes are provided on the ceramic member to which the housing is joined, and conductive pins mainly composed of platinum are inserted through and fixed to the through-holes. Titanium has been used as a highly biocompatible metal and has been increasingly used in a state in which it is joined to a ceramic member, as in the feedthrough described in Patent Literature 1.